SIM900A的EAT开发，文档中的源码实现功能比较多。Adc，audio play,csd,customerATCommand,DTMF,fcm,flash,gpio,gpio interrupt,http,i2c,keypad,pwm,serialPortStatus,SIM_MUX,sms,socket,spi,spienhance,system,TCP,timer,update,urc-SIM900A EAT development, in the document source mor